Cell death after a cerebrovascular accident or brain stroke is the result of the complex interaction of excitotoxicity, acidosis, inflammation, oxidative stress, peri infarct depolarization and apoptosis.
The term apoptosis is used as a synonym of programmed cell death (hereinafter, PCD); however, apoptosis was originally defined as a set of morphological changes which occur after PCD. In developing neurons, these changes include condensation and excision of chromatin and the formation of the so-called apoptotic bodies. These changes are different from the morphological changes which characterize the inflammation caused by necrosis of the cytoplasmic organelles and the breaking of the mitochondrial and cytoplasmic membrane.
A mild ischemic injury normally induces cell death through an apoptotic-like mechanism instead of through necrosis. Apoptosis activators include oxygen free radicals, linking with death receptors, DNA damage, protease activation and ionic balance disadjustment. Several experimental studies have shown that the inhibition of apoptosis reduces the seriousness of the ischemic lesion.
The activation of caspases is a consequence of mitochondrial apoptosis. The mitochondrial dysfunction and the opening of the mitochondrial transitory permeability pore can result in activation of caspases through the exit of cytochrome C towards the cytoplasm; however, there are other different mechanisms through which mitochondrial dysfunction can contribute to ischemic neuronal death. The seriously damaged mitochondria can be incapable of maintaining the electrochemical gradient necessary for breathing and glucose oxidation. In this way, the mitochondrial dysfunction can aggravate the ischemic injury by exacerbation of the energetic failure. The dysfunctional mitochondria also produces oxygen free radicals which injure other cell organelles and DNA. Therefore, the treatments preventing mitochondrial dysfunction could also be a more powerful neuroprotective strategy than caspase inhibition.
High levels of intracellular Ca2+, Na+ and ADP make the mitochondria produce harmful levels of oxygen reactive species. Unlike other organs, the brain is particularly vulnerable to oxygen reactive species since the neurons have relatively low levels of endogenous antioxidants. The abundance of oxygen radicals causes the destruction of cell macromolecules and they participate in signaling mechanisms which produce apoptotic cell death. Ischemia activates nitric oxide synthase (hereinafter, NOS) and increases the generation of nitric oxide (hereinafter, NO), which is combined with super oxide to produce peroxynitrite, a powerful oxidation agent. The production of NO and oxidative stress are also linked to the over activation of poly(ADP-ribose)polymerase-1 (hereinafter, PARP-1), an enzyme for DNA repair.
After the reperfusion, there is an increase in the production of super oxide, NO and peroxynitrite. The formation of these radicals in the proximity of blood vessels plays an important role in the injury induced by reperfusion. These radicals activate the metalloproteases (hereinafter, MMP), which degrade collagen and laminins in the basal lamina, break the integrity in the vascular wall and increase permeability of the hematoencephalic barrier (hereinafter, HEB). Oxidative and nitrosilative stress also activate the recruiting and migration of neutrophils and other leucocytes to the brain vasculature, which release enzymes which additionally increase degradation in the basal lamina and vascular permeability. These events can produce a parenchymatous haemorrhage, vasogenic cerebral oedema and leukocyte infiltration inside the brain.
Uric acid is a potent antioxidant which blocks the reaction between superoxide anion and nitric oxide, which damages the cells when nitrosylating thyroxine residues of proteins. Plasmatic concentration of uric acid is almost 10 times higher than that of other antioxidant substances, such as vitamins C or E, and its antioxidant capacity is higher. Besides, uric acid prevents the degradation of extra cellular superoxide dismutase, which is an essential enzyme for normal endothelial functioning. In culture of hippocampus cells, uric acid protects against excitotoxic damage by glutamate, stabilizing calcium homeostasis and preserving the mitochondrial function. Uric acid has also shown the inhibition of the Fenton reaction.
In an adult rat, the administration of uric acid 24 hours before the occlusion of the middle cerebral artery or 1 hour after the reperfusion significantly reduces the resulting cerebral infarction, suppresses reactive oxygen species accumulation and reduces lipid peroxidation (Yu Z F, et al. Uric acid protects neurons against excitotoxicf and metabolic insults in cell culture, and against focal ischemic brain injury in vivo; J Neurosci Res 1998; 53:613-25). Uric acid administration is neuroprotective in a thromboembolism model of focal cerebral ischemia of a rat and this neuroprotective effect is synergic with respect to the beneficial effect attained by rtPA (Romanos E, Planas A M, Amaro S, Chamorro A. Uric acid reduces brain damage and improves the benefits of rt-PA in a rat model of thromboembolic stroke. J Cereb Blood Flow Metab. 2007; 27:14-20).
There are studies which show the existing relation between higher levels of uric acid in blood in the moment of a brain stroke and a reduced neurological seriousness caused by said brain stroke.
In addition, the recent study URICO-ICTUS (Clinical study phase 2b/3) showed that the use of uric acid in combination with the standard thrombolytic treatment (alteplase) is safe. Nevertheless, in this study the combined therapy did not show an statistically significant effect and, hence, the conclusion of the study is that no change was seen in the proportion of patients with excellent results at 90 days (Chamorro A, Amaro S, Castellanos M, Segura T, Arenillas J, Martí-Fábregas J, Gállego J, Krupinski J, Gomis M, Cánovas D, Carné X, Deulofeu R, Román L S, Oleaga L, Torres F, Planas A M; URICO-ICTUS Investigators. Safety and efficacy of uric acid in patients with acute stroke (URICO-ICTUS): a randomised, double-blind phase 2b/3 trial. Lancet Neurol. 2014; 13:453-60).
Finally, the PCT Patent application WO2010112113 discloses the combined use of uric acid and citicoline for the treatment of ictus, demonstrating their effects in cell cultures models of ischemia.
Therefore, given the complexity of the treatment of brain stroke and the absence of a therapy that allows its effective treatment, there is still a need to investigate in new therapies or combinations thereof that allow an increase not only in the survival rate of the patients of brain stroke but also, and more importantly, that allow to improve the conditions in which such patients survive (increasing their functional independence, reducing brain damage, etc.).
The inventor of the present invention, after extensive and exhaustive research, have surprisingly seen that the administration of uric acid in patients with brain stroke that are or have been treated by means of mechanical thrombectomy shows a synergistic effect and allows to improve the positive results obtained in said patients, drastically and significantly improves the outcome of the patients, increase their functional independence and decrease the damaged brain area., contributing, hence, to solve the problem present in the state of the art and mentioned above.